1. Field of the Invention
The present invention relates to an optical fiber cutter which cuts an optical fiber according to the principle of stress-rupture.
2. Description of the Related Art
A cutting method based on the principle of stress-rupture is used to cut an optical fiber wire in which either a core and a cladding are both made of glass, or only a core is made of glass. According to this cutting method, tension is applied to the optical fiber wire, and then a movable blade is used to impart a crack in an outer periphery of the wire while under tension. Using the crack as the starting point, a stress rupture in the wire is caused. Then, the wire is cut in a direction perpendicular to an axis of the wire, so as to obtain a cutting surface having a high degree of flatness.
A description will be now given of a related optical fiber cutter using the principle of stress-rupture with reference to FIGS. 11A and 11B. An optical fiber wire (not shown) is inserted into and secured to a ferrule (not shown), and then a cutter cuts a portion of the fiber that is projected from a tip end of the ferrule. This cutter also uses the stress-rupture principle in that, when a tension or stress is applied to a glass having a crack, the crack is progressed and the glass is split to create a flat surface that is perpendicular to a tensional direction.
This cutter has a diamond blade 5, a steel follower blade 31 opposing the blade 5, a mechanism which interposes the optical fiber wire between the both blades so as to provide an initial crack in the optical fiber wire, and a mechanism which applies tension to the optical fiber wire.
In the cutting of the wire, the ferrule with the projected optical fiber wire is fitted into a ferrule insertion portion 7 which is attached to a lower surface of a base 1, and then the optical fiber wire is arranged between clamp pieces 17. When a lever 3, which is supported by a frame 2, is rotated in a direction of the arrow shown in FIG. 11B, a slide block 16 connected to the lever 3 through a tension spring 12 is lifted up along a guide shaft 15. In accordance with the motion of the slide block 16, the clamp pieces 17 separate from a reverse V-shaped guide 9, and then close an opening between them so as to hold the optical fiber wire. The slide block 16 is lifted up while the clamp pieces 17 hold the optical fiber wire, so as to apply tension to the optical fiber wire.
Further, when the lever 3 is rotated, a pair of blade holders 24 are closed through a pressing piece 23 by means of a pin 11 located at an end of the lever 3. Thus, the distance between the blade 5 and a follow blade 31 respectively held in the blade holders 24 is narrowed. The optical fiber wire is caught by the blade 5 and the follow blade 31 in a horizontal direction which is perpendicular to an axial direction of the optical fiber wire, so that an initial crack is provided in the optical fiber wire. When tension is applied to the optical fiber wire, the initial crack progresses, and the optical wire is cut.
The above cutter cuts the optical fiber wire by interposing the fiber between the blade and the follow blade. However, it is realistically difficult to interpose the optical fiber wire in such a manner that the blade and the follow blade confront each other precisely. If there is a small gap between the blades during the confronting state, a stress directed in a direction other than the horizontal direction is undesireably applied to the optical fiber wire. As a result, the optical fiber wire is cut with a inclined surface with respect to the tip end surface of the ferrule, or, the application of the stress results in the optical fiber wire having a non-flat cut surface.
There is another cutting method which is based on the same stress-rupture principle, but which performs the steps in a different order. In this method, the optical fiber wire is first cracked. Next, a tension is applied to the optical fiber wire, to thereby cut the wire. The optical fiber wire is thereafter inserted and secured to the ferrule.
However, this method also has some problems which result in the cutting surface of the optical fiber wire being damaged, and difficulty in flatly securing the tip end surface of the ferrule and the cutting surface of the optical fiber wire.
FIGS. 12 to 13B show other related optical fiber cutters. In the cutter shown in FIG. 12, a movable blade 121 is inserted inside a fixing holder 120. The movable blade 121 is moved projectably through a spring 122 by pressing a button 123, so that an optical fiber wire a to which the tension is applied is cut by the movable blade 121 in conjunction with a follow blade 127.
In the cutter shown in FIGS. 13A and 13B, a button 125 for pushing the movable blade 121 can regulate movement of the movable blade 121 with respect to a mount 124 to a predetermined value. The movable blade 121 is inserted projectably into the button 125. Further, there is provided a blade pressure adjusting screw 126 and a spring 122, which is disposed between the screw 126 and the movable blade 121. In this structure, the optical fiber wire a to which the tension is applied is disposed on a guide groove 128, shown in FIG. 13B, and the wire a is cut by pressing the button 125. (This cutter is disclosed in Japanese Patent Unexamined Publication No. Sho 59-142503.)
The cutter shown in FIG. 12 requires the button 123 to be pushed by hand and transmits this pushing force to the movable blade 121, so as to cut the optical fiber wire a. However, the pushing force applied to the button 123 varies in accordance with a personal force level. Although the spring 122 functions as a cushioning device for preventing the optical fiber wire a from being cut too deeply by the movable blade 121, both the button 123 and the movable blade 121 move freely. Therefore, the structure of FIG. 12 has many indeterminate factors, and thus cannot stabilize a force upon cutting.
The cutting surface of the optical fiber wire is influenced by the force. Since a cutting depth of the blade varies in accordance with the irregularity of the force, the scattering loss of the transmitting light at the cutting surface may be large.
On the other hand, in the cutter of FIGS. 13A and 13B, since the amount of movement of the button 125 is regulated and the blade pressure can be adjusted by the screw 126, the influence according to the pushing level of the button 125 or the like is small. However, this cutter requires that the screw 126 is adjusted prior to actually cutting the optical fiber wire. And then, after observing a state of the cutting surface, the blade pressure is readjusted to obtain a better cutting surface. Accordingly, the operation for the cutter of FIGS. 13A and 13B is complicated.
In addition, the adjusting screw 126 may loosen when the cutter is used or carried. In such a case, the optical fiber wire may be cut after the adjusting screw has deviated from its proper position, or the screw 126 may need to be readjusted.
Further, even if the adjusting value is retained at a regulated value, the blade pressure may differ when a cutting operation is conducted by a person other than the adjuster. Accordingly, the cutting is unstable.
Moreover, the movable blade cuts the optical fiber wire in conjunction with the follow blade or the guide groove. Therefore, a stress may be applied in a direction other than a horizontal direction, which is perpendicular to the axis of the wire, to thereby form the non-flat cutting surface.